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| 型号： | LP5521YQX/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 13/44页 |
| 文件大小： | 0K |
| 描述： | IC LED DRIVER RGB 24-LLP |
| 标准包装： | 4,500 |
| 系列： | PowerWise® |
| 恒定电流： | 是 |
| 拓扑： | PWM，切换式电容器（充电泵） |
| 输出数： | 3 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 背光，照明管理装置（LMU） |
| 类型 - 次要： | RGB |
| 频率： | 1.25MHz |
| 电源电压： | 2.7 V ~ 5.5 V |
| 输出电压： | 4.55V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 24-WFQFN 裸露焊盘 |
| 供应商设备封装： | 24-LLP |
| 包装： | 带卷 (TR) |
| 工作温度： | -30°C ~ 85°C |
| 其它名称： | LP5521YQX |
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SNVS441F – JANUARY 2007 – REVISED FEBRUAY 2013
FUNCTIONAL DESCRIPTION
CHARGE PUMP OPERATIONAL DESCRIPTION
OVERVIEW
The LP5521 includes a pre-regulated switched-capacitor charge pump with a programmable voltage
multiplication of 1 and 1.5x.
On 1.5x mode by combining the principles of a switched-capacitor charge pump and a linear regulator, it
generates a regulated 4.5V output from Li-Ion input voltage range. A two-phase non-overlapping clock generated
internally controls the operation of the charge pump. During the charge phase, both flying capacitors (C FLY1 and
C FLY2 ) are charged from input voltage. In the pump phase that follows, the flying capacitors are discharged to
output. A traditional switched capacitor charge pump operating in this manner will use switches with very low on-
resistance, ideally 0 ? , to generate an output voltage that is 1.5x the input voltage. The LP5521 regulates the
output voltage by controlling the resistance of the input-connected pass-transistor switches in the charge pump.
OUTPUT RESISTANCE
At lower input voltages, the charge pump output voltage may degrade due to effective output resistance (R OUT ) of
the charge pump. The expected voltage drop can be calculated by using a simple model for the charge pump
illustrated in following figure.
Charge Pump
V IN
REG
9?
1.5 x
1.5 [ 9?
V OUT
R OUT
Figure 23.
The model shows a linear pre-regulation block (REG), a voltage multiplier (1.5x), and an output resistance
(R OUT ). Output resistance models the output voltage drop that is inherent to switched capacitor converters. The
output resistance is 3.5 ? (typ), and is function of switching frequency, input voltage, flying capacitors’
capacitance value, internal resistances of switches and ESR of flying capacitors. When the output voltage is in
regulation, the regulator in the model controls the voltage V’ to keep the output voltage equal to 4.5V (typ). With
increased output current, the voltage drop across R OUT increases. To prevent drop in output voltage, the voltage
drop across the regulator is reduced, V’ increases, and V OUT remains at 4.5V. When the output current increases
to the point that there is zero voltage drop across the regulator, V’ equals the input voltage, and the output
voltage is “on the edge” of regulation. Additional output current causes the output voltage to fall out of regulation,
so that the operation is similar to a basic open-loop 1.5x charge pump. In this mode, output current results in
output voltage drop proportional to the output resistance of the charge pump. The out-of-regulation output
voltage can be approximated by: V OUT = 1.5 x V IN – I OUT x R OUT .
CONTROLLING CHARGE PUMP
Charge pump is controlled with two CP_MODE bits in register 08H. When both bits are low, charge pump is
disabled and output voltage is pulled down with 300 k ? . Charge pump can be forced to bypass mode, so battery
voltage is going directly to RGB outputs. In 1.5x mode output voltage is boosted to 4.5V. In automatic mode,
charge pump operation mode is defined by LED outputs saturation like described in LED Forward Voltage
Monitoring. In following table are listed operation modes and selection bits.
Table 1. CONFIG register (08H):
Name
CP_MODE
Bit
4:3
Description
Charge Pump Operation Mode
00b = OFF
01b = Forced to bypass mode (1x)
10b = Forced to 1.5x mode
11b = Automatic mode selection
Copyright ? 2007–2013, Texas Instruments Incorporated
Product Folder Links: LP5521
13
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